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emphasized textThe term $B_{4/2}$ anomaly is used in relation to even-even nuclei in which the ratio of the B(E2) transition rates $B_{4/2} = B(E2; 4_1^+\to 2_1^+)/ B(E2; 2_1^+\to 0_1^+)$ is less than unity, a value contrary to the predictions of all collective models. A few experimental examples have been found over the last years, the best known ones being $^{166}$W [1], $^{168,170}$Os [2,3], $^{172}$Pt [4]. From the phenomenological point of view, it has been shown that the effect can be accommodated within the Interacting Boson Model-1 (IBM-1), in which no distinction between valence protons and neutrons is made, through the inclusion of 3-body and 4-body interactions [5,6]. Alternatively, it can be interpreted [7] within the SU(3)* dynamical symmetry of IBM-2, in nuclei in which the valence protons correspond to holes and the valence neutrons to particles, or vice versa. Ongoing efforts [8] for the first microscopic interpretation of the effect, within covariant density functional theory employing the DDME2 energy density functional, will be reported.
[1] B. Saygi et al., Phys. Rev. C 96, 021301(R) (2017).
[2] T. Grahn et al., Phys. Rev. C 94, 044327 (2016).
[3] A. Goasduff et al., Phys. Rev. C 100, 034302 (2019).
[4] B. Cederwall et al., Phys. Rev. Lett. 121, 022502 (2018).
[5] Y.-X. Cheng, D.-H. Zhao, Y.-Y. Shao, L. Gong, T. Wang and X.-S. Kang,
Chin. Phys. C 49, 104105 (2025).
[6] Y. Zhang and W. Teng, Phys. Rev. C 111, 014324 (2025).
[7] W. Teng, Y. Zhang, S.-N. Wang, F. Pan, C. Qi, and J. P. Draayer,
Phys. Lett. B 865, 139487 (2025).
[8] D. Bonatsos, K. E. Karakatsanis, and P. Vasileiou, in preparation.
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